1. Field of the Invention
The present invention generally relates to packaging structures for light emitting diodes, and more particularly to a flip-chip packaging structure and a related method for light emitting diodes with enhanced heat dissipating efficiency.
2. The Prior Arts
Light emitting diodes (LEDs) have advantages of small size, low power consumption, long operation life, and therefore will substitute light bulbs or fluorescent lamps in the future as the mainstream light source. However, to enhance the brightness of LEDs, it is necessary to increase power, numbers, or density of LEDs. These will inevitably increase the heat produced by the LEDs. This heat, if not effectively dissipated, will damage the LEDs themselves, shorten their operation life, and affect their brightness.
To improve heat dissipation, a packaging structure as shown in FIG. 1 has been adopted. As illustrated, LED 10 is attached to an aluminum substrate 20 by eutectic bonding with a eutectic layer 30 interposed therebetween. An insulating layer 21 is formed in specific areas on top of the aluminum substrate 20. Bonding pads 22 are in turn formed on top of the insulating layer 21, which are electrically connected to the first and second electrodes 11 and 12 of the LED 10 respectively via bonding wires 23. In this conventional approach, even though the eutectic layer 30 is able to dissipate the heat produced by the LED 10 through the aluminum substrate 20 by conduction, the sapphire substrate 13 of the LED 10 has inferior thermal conductivity and the heat dissipation efficiency is therefore impaired. Furthermore, the packaging structure described above has the first electrode 11 and the second electrode 12 both formed on the top of LED 10 which blocks light emitted from LED 10 and decreases its brightness.
To overcome the foregoing problems, a flip-chip packaging structure as shown in FIG. 2 is adopted, where LED 10 is reversed and attached to a printed circuit board (PCB) 40. The PCB 40 has bonding pads 41 formed on specific locations on the top surface, and the bonding pads 41 are electrically connected to bonding wires 42. The first and second electrodes 11 and 12 of the LED 10 are connected separately to bonding pads 41 using metallic bumps 43. Although the packaging structure indeed avoid blocking light emitted from LED, heat generated by the LED 10 can only be conducted to the PCB 40 through the small contact area with the metallic bumps 43. Additionally, the PCB 40 itself has limited thermal conductivity and cannot provide satisfactory help to the heat dissipation.